1. Field of the Invention
The present invention relates to an electric motor having a rotation detection sensor and, more particularly, to an electric motor suitable for use in a vehicle power seat apparatus.
2. Related Art
In a conventional motor, as shown in FIG. 12, a rotor 53 is disposed within a yoke 51 and a housing 52. The rotor 53 includes an armature 55, commutator 56, worm 57 and permanent magnet 58, all of which are fixedly mounted on a rotary shaft 54. The armature 55 is disposed generally centrally within the yoke 51 in the axial direction. The commutator 56 is disposed at a motor-side end position of the housing 52, where power supply brushes 59 are disposed. The worm 57 is disposed generally centrally within the housing 52 in the axial direction. The permanent magnet 58 is disposed between the worm 57 and one end of the rotary shaft 54. Both ends of the rotary shaft 54 are supported rotatably by a pair of bearings 60.
A sensor accommodation recess 52a is formed on the outer periphery of the housing 52 at a position corresponding to the permanent magnet 58. A sensor circuit plate 61 is fixedly mounted in the recess 52a, so that a Hall IC device 62 is provided on the circuit plate 61 at a position where it faces the permanent 58. The circuit plate 61 is fixed to the housing 52 by a toothed washer 3.
The recess 52a is filled with a silicone bond 7 to seal and protect the circuit plate 61 from foreign materials such as water and dust. Electric leads 65 connected to the circuit plate 61 are arranged to extend from the central part of the housing 52 to the outside of the housing 52. A protective cover 66 is fitted by a toothed washer 67 to cover the recess 52a and the electrical leads 65.
In this motor, the worm 57 and the permanent magnet 58 rotate with the rotary shaft 54 when the rotor 53 rotates, so that a worm wheel (not shown) disposed in engagement with the worm 57 is driven by the worm 57. As the direction of the magnetic field generated by the permanent magnet 58 changes with the rotation of the permanent magnet 58, the Hall IC device 62 generates an output signal indicative of rotation of the rotary shaft 54 in response to reversal in the direction of the magnetic field. This output signal is applied through the electrical leads 65 to an electronic control unit (not shown), so that the motor is feedback controlled by the control unit.
In this motor, however, the rotation detection sensor requires a number of component parts such as the accommodation recess 52a, circuit plate 61, silicone bond 64 and toothed washer 63, resulting in increase in the parts assembling work and increase in the production cost. Further, it is difficult to replace the circuit plate 61 by a new one, when the rotation detection sensor fails to operate.
As the electric leads 65 are arranged to extend along the outside of the housing 52, it requires troublesome lead arranging work. Further, as the leads 65 are likely to receive radiation noise as an antenna, the motor control by the control unit is likely to be influenced by the noise superimposed on the output signal of the Hall IC device 62. Still further, as the electric leads are exposed to the outside from the housing 52 and the protection cover 66, the electric leads 65 are cut or shorted when the motor is installed into a limited space (e.g., power seat) in a vehicle.